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falconmaster 13-01-2017 14:52

Thin rope!
 
We have been discussing on our team how a thin rope will be attached on the air ship. With a thick rope its the knot that keeps it from sliding through the two tabs with the pin through it. If you use a thin rope, do you have to make a really big knot? Or can you make a loop and hook it to something? Anybody out there know? Thanks in advance!

ATannahill 13-01-2017 14:57

Re: Thin rope!
 
You are required to have a retaining feature greater than 1 inch in your rope.

Quote:

Originally Posted by I04-E Blue Box
To interface with the field a ROPE must have a retaining feature (e.g. a knot) greater than 1 in. (~25.4 mm) in diameter to interface with the DAVITS (RF).


Jonny_Jee 13-01-2017 15:01

Re: Thin rope!
 
Take a look at the monkeys fist knot. It's pretty large and depending on the number of windings you do, can be as large as you'd like. Also they look really cool!

falconmaster 13-01-2017 15:12

Re: Thin rope!
 
Quote:

Originally Posted by ATannahill (Post 1630662)
You are required to have a retaining feature greater than 1 inch in your rope.

So if using a thin rope, like 1/8 or 1/4" then you must make enough knots to be greater than 1"? You cannot make a loop to hook it on the airship?

SenorZ 13-01-2017 15:20

Re: Thin rope!
 
It looks like a Slot that the knot sits in, so if you have a thin rope, with a thin knot, it will slip through.

chrisrin 13-01-2017 15:30

Re: Thin rope!
 
Something like this? http://www.sky-international.com/pro...e-ball-fenders

engunneer 13-01-2017 15:32

Re: Thin rope!
 
Quote:

Originally Posted by chrisrin (Post 1630679)

that is not a legal rope component.

chrisrin 13-01-2017 15:33

Re: Thin rope!
 
Just realized those things are huge. Some shaped like that would work. Maybe a disc swing could be used as the top anchor? Or would that be too big?

chrisrin 13-01-2017 15:37

Re: Thin rope!
 
Quote:

Originally Posted by engunneer (Post 1630682)
that is not a legal rope component.

Yes if the larger-than-1-inch retaining feature must be part of the ROPE, then I guess a knot it is.

EmileH 13-01-2017 15:38

Re: Thin rope!
 
Quote:

Originally Posted by chrisrin (Post 1630684)
Just realized those things are huge. Some shaped like that would work. Maybe a disc swing could be used as the top anchor? Or would that be too big?

It is not made of non-metallic, woven fibers, so it is not legal to be a part of the rope.

AdamHeard 13-01-2017 15:51

Re: Thin rope!
 
We're looking at a .301" diameter rope a that should spool very nicely, but I'm afraid of looking back and thinking we could've done more.

s_forbes 13-01-2017 16:11

Re: Thin rope!
 
Quote:

Originally Posted by AdamHeard (Post 1630697)
We're looking at a .301" diameter rope a that should spool very nicely, but I'm afraid of looking back and thinking we could've done more.


Richard Wallace 13-01-2017 16:19

Re: Thin rope!
 
Quote:

Originally Posted by s_forbes (Post 1630720)

Can you please convert lmao to SI units (m/sec^2)? :rolleyes:

Richard Wallace 13-01-2017 16:30

Re: Thin rope!
 
Quote:

Originally Posted by Jonny_Jee (Post 1630666)
Take a look at the monkeys fist knot. It's pretty large and depending on the number of windings you do, can be as large as you'd like. Also they look really cool!

+1^



The image above is a three-strand monkey's fist in 3/8" braided polyester rope. Knot diameter ~2.3 inch.

Rep points to the first student who ties one, measures the length of rope required between the two taped points, and posts a correct result (+/- 30 mm).

jnicho15 13-01-2017 16:47

Re: Thin rope!
 
Quote:

Originally Posted by Richard Wallace (Post 1630733)
...3/8"...
...~2.3 inch.
...(+/- 30 mm).

One of these things is not like the other...

Richard Wallace 13-01-2017 16:49

Re: Thin rope!
 
Quote:

Originally Posted by jnicho15 (Post 1630745)
One of these things is not like the other...

If you can figure out the knot, I think you can also figure out unit conversion.

Ian H. 13-01-2017 17:27

Re: Thin rope!
 
I was under the assumption that the retaining feature could be a loop and/or knot. Because the davit has 2 steel fingers, with the manual saying:

These fingers are 1¼ in. (~3 cm) apart and
have a hole for a locking pin. The ROPE passes through the fingers with the top knot on the AIRSHIP
side of the fingers.

This phrasing implies that there has to be a knot, because the top knot is on the AIRSHIP side of the fingers, but part of me thinks this only is referring to the rope installed on the field. But the definition of ROPE, seems to imply otherwise.

However, the black rope in the picture in IO4 has 2 loops:



and IO4 E says:

E. be configured such that it engages securely with the FIELD.
To interface with the field a ROPE must have a retaining feature (e.g. a
knot) greater than 1 in. (~25.4 mm) in diameter to interface with the
DAVITS (RF).


This seems to say something other than a knot is allowed.

There seems to be contradicting info, but if a loop is allowed it seems like you could just put a loop around one of the steel fingers on the davit and it would still pass through the fingers

chrisrin 13-01-2017 17:42

Re: Thin rope!
 
Frankly, from a safety standpoint, I'm surprised a 100% safe method for securing the rope at the top isn't being required. If a team uses a thin rope with a knot they presume is thick enough but isn't under certain scenarios (e.g. hanging robot actually bumped by another robot), then the hanging robot could fall to the ground with the current guidelines. A worse scenario would be the robot falling on a person because the top knot slipped through the 1" opening after the match when students are trying to extract their robot. There are many types of rope/cord out there with different characteristics. It would have been far safer IMO to include in the KoP a 100% reliable plastic anchor compatible with any (within reason) type of rope OR to require a loop at the top and usage of the fingers mentioned in the previous post.

KevinG 13-01-2017 17:49

Re: Thin rope!
 
Quote:

Originally Posted by chrisrin (Post 1630783)
Frankly, from a safety standpoint, I'm surprised a 100% safe method for securing the rope at the top isn't being required. If a team uses a thin rope with a knot they presume is thick enough but isn't under certain scenarios (e.g. hanging robot actually bumped by another robot), then the hanging robot could fall to the ground with the current guidelines. A worse scenario would be the robot falling on a person because the top knot slipped through the 1" opening after the match when students are trying to extract their robot. There are many types of rope/cord out there with different characteristics. It would have been far safer IMO to include in the KoP a 100% reliable plastic anchor compatible with any (within reason) type of rope OR to require a loop at the top and usage of the fingers mentioned in the previous post.

Stuff like this is going to fall on the RI to approve. Presumably the RI would notice that the knot is not sufficiently robust and would instruct the team to correct it. Given the safety issue I suspect this will become a point of emphasis. FIRST has already provided a safe method of securing the rope to the field, and it seems fairly robust and simple too. Most people should be able to knot a rope to a minimum of 1" width.

Personally I'm surprised that the GDC hasn't implemented a minimum width for this exact reason. Maximum 1", minimum 0.5", for example.


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